Pneumatic radial tire with polyethylene terephthalate cord belt reinforcing layer

ABSTRACT

This invention relates to a pneumatic radial tire having low road noise and flat spot and a high high-speed durability, and more particularly to a pneumatic radial tire comprising a radial carcass ( 5 ), a belt ( 6 ) disposed outside a crown portion of the carcass in a radial direction and comprised of at least two belt layers, and a belt reinforcing layer ( 7 A,  7 B) disposed outside the belt in the radial direction, characterized in that the belt reinforcing layer  7 A,  7 B is formed by continuously and spirally winding a polyethylene terephthalate cord(s) in a circumferential direction of the tire, and this cord has an elastic modulus of not less than 2.5 mN/dtex·% under a load of 29.4 N measured at 160° C.

TECHNICAL FIELD

This invention relates to a pneumatic radial tire, and more particularlyto a pneumatic radial tire having low road noise and flat spot and ahigh high-speed durability.

BACKGROUND ART

Currently, at least two belt layers containing steel cords arrangedslantly at a certain cord angle with respect to an equatorial plane of atire are mainly used in a belt of a radial tire for a passenger car suchthat the cords of these layers are crossed with each other. Also, a beltreinforcing layer comprising nylon cords or the like is disposed on anoutside of the belt in a radial direction in order to ensure thestability during the running of the tire and particularly prevent thepeeling of the belt layer in the high-speed running (particularly,peeling notably produced at an end portion of the belt layer) to improvethe durability.

At the present day, it is common to adopt the belt reinforcing layer forimproving the high-speed durability. As a material of the cord in thebelt reinforcing layer is mainly used a nylon being low in the heatbuild-up and cost. In the radial tire having such a belt reinforcinglayer, however, it is recently demanded to further reduce the road noiseand flat spot and improve the pushing-out property at the end portion ofthe belt in the high-speed running.

As such a countermeasure, a high-elastic cord composed of an aromaticpolyamide (aramid) or the like, which has an elasticity higher than thatof the nylon and a high glass transition point (Tg) and is effective forthe lowering of the road noise and flat spot, is applied to the beltreinforcing layer. However, the high-elastic cord has a problem in viewof the cost because it is expensive.

Moreover, as a material having an elasticity higher than that of thenylon but being low in the cost is known a polyethylene terephthalate(PET). However, the polyethylene terephthalate is large in the loweringof the elastic modulus at higher temperatures, and has a problem thatthe sufficient effect of suppressing the pushing-out cannot be developedas the temperature of the tire elevates during the high-speed running.Since a filament composed of the polyethylene terephthalate does nothave a functional group on its surface, the adhesiveness to rubber isremarkably inferior as compared with that of the nylon in the adhesivetreatment with a usual RFL adhesive liquid. Therefore, the use of thepolyethylene terephthalate in the belt reinforcing layer can lower theroad noise and flat spot, but has a problem that the high-speeddurability deteriorates notably.

On the contrary, in order to improve the high-speed durability of thetire wherein the cords made of the polyethylene terephthalate are usedin the belt reinforcing layer, there are proposed many means forimproving the adhesiveness between cord and rubber (JP-A-2001-9927,JP-A-2001-63312, JP-A-2001-98245 and JP-A-2000-248254).

SUMMARY OF THE INVENTION

However, even if the adhesiveness of the polyethylene terephthalatecords is improved by the means described in the above patent documents,it is still inferior to the adhesiveness of the nylon cords, so that thetire using the polyethylene terephthalate cords in the belt reinforcinglayer is still inferior in the high-speed durability to the tire usingthe nylon cords in the belt reinforcing layer.

It is, therefore, an object of the invention to solve theabove-mentioned problems of the conventional techniques and to provide apneumatic radial tire wherein the polyethylene terephthalate cord isapplied to the belt reinforcing layer and the high-speed durability isimproved.

The inventor has made various studies in order to achieve the aboveobject and discovered that the pushing-out degree of the belt in thehigh-speed running can be suppressed by defining an elastic modulus ofthe polyethylene terephthalate cord to a certain value or more in thetire using such a cord in the belt reinforcing layer and also the stressat the leading-trailing time of the tire can be decreased to improve thehigh-speed durability of the tire, and as a result the invention hasbeen accomplished.

That is, the pneumatic radial tire according to the invention is apneumatic radial tire comprising a radial carcass, a belt disposedoutside a crown portion of the carcass in a radial direction andcomprised of at least two belt layers, and a belt reinforcing layerdisposed outside the belt in the radial direction, and is characterizedin that the belt reinforcing layer is formed by continuously andspirally winding a polyethylene terephthalate cord(s) in acircumferential direction of the tire, and this cord has an elasticmodulus of not less than 2.5 mN/dtex·% under a load of 29.4 N measuredat 160° C.

In the invention, the elastic modulus under the load of 29.4 N measuredat 160° C. is calculated by converting a gradient of a tangent (N/%) ina load-elongation curve of the cord measured at 160° C. at a pointcorresponding to the load of 29.4 N into a value per 1 dtex. At thispoint, the gradient of the tangent in the load-elongation curve at thepoint corresponding to the load of 29.4 N means a gradient of a tangentS in a load-elongation curve C of the cord at a point corresponding tothe load of 29.4 N as shown in FIG. 1.

In a preferable embodiment of the pneumatic radial tire according to theinvention, the cord is treated with an adhesive composition comprising athermoplastic polymer (A), a heat-reactive aqueous polyurethane resin(B) and an epoxy compound (C), wherein a main chain of the thermoplasticpolymer (A) does not substantially have an addition-reactivecarbon-carbon double bond but has at least one crosslinkable functionalgroup as a pendant group.

In another preferable embodiment of the pneumatic radial tire accordingto the invention, the cord is treated with an adhesive compositioncomprising a thermoplastic polymer (A), a heat-reactive aqueouspolyurethane resin (B), an epoxy compound (C) and a rubber latex (D),wherein a main chain of the thermoplastic polymer (A) does notsubstantially have an addition-reactive carbon-carbon double bond buthas at least one crosslinkable functional group as a pendant group.

At this moment, it is more preferable that the main chain of thethermoplastic polymer (A) is composed of an ethylenically additionpolymer mainly having a straight-chain structure and/or a polyurethanebased polymer, and the crosslinkable functional group as a pendant groupis at least one selected from the group consisting of an oxazolinegroup, a bismaleimido group, a (blocked) isocyanate group, an aziridinegroup, a carbodiimido group, a hydrazino group, an epoxy group and anepithio group.

In the other preferable embodiment of the pneumatic radial tireaccording to the invention, the cord is subjected to an adhesivetreatment (dip treatment) under a tension of not less than 6.9×10⁻²N/dtex.

In a further preferable embodiment of the pneumatic radial tireaccording to the invention, the cord has a twisting coefficient α of500-2500 defined by the following equation (I):α=T×D ^(1/2)  (I)(wherein α is a twisting coefficient, T is a twisting number and D is atotal fineness (dtex) of the cord).

In another preferable embodiment of the pneumatic radial tire accordingto the invention, the cord has an elongation percentage of not more than2% in the tire after vulcanization with respect to an original length ofthe cord before vulcanization.

In the other preferable embodiment of the pneumatic radial tireaccording to the invention, the cord has a total fineness of 1000-3500dtex.

According to the invention, the pneumatic radial tire having an improvedhigh-speed durability can be provided by defining the elastic modulus ofthe polyethylene terephthalate cord used in the belt reinforcing layerof the tire to a certain value or more. In the tire, the pushing-outdegree in the high-speed running is suppressed and the stress inleading-trailing time of the tire is decreased, so that thedeterioration of the high-speed durability due to a lack of adhesivenessbetween the cord and the rubber as compared to the nylon cords issufficiently compensated. Furthermore, the adhesiveness between the cordand the rubber at high temperatures can be improved by treating the cordwith the adhesive composition containing the specific compound tofurther improve the high-speed durability.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 shows a load-elongation curve of a cord.

FIG. 2 is a cross-sectional view of an embodiment of the pneumaticradial tire according to the invention.

BEST MODE FOR CARRYING OUT THE INVENTION

The invention will be described in detail below. The pneumatic radialtire of the invention comprises a radial carcass, a belt disposedoutside a crown portion of the carcass in a radial direction andcomprised of at least two belt layers, and a belt reinforcing layerdisposed outside the belt in the radial direction, and is characterizedin that the belt reinforcing layer is formed by continuously andspirally winding a polyethylene terephthalate cord(s) in acircumferential direction of the tire, and this cord has an elasticmodulus of not less than 2.5 mN/dtex·% under a load of 29.4 N measuredat 160° C. At this moment, the reason why the elastic modulus ismeasured at 160° C. is due to the fact that as the temperature insidethe tire rises according to the high-speed running, the temperature ofthe belt reinforcing layer reaches at 160° C. at a time of causing thetire trouble in the high-speed running test. Particularly, the elasticmodulus of the polyethylene terephthalate cord at higher temperatureshas an important meaning because such a cord is large in the lowering ofthe elastic modulus at an elevated temperature as compared to a roomtemperature and cannot develop the effect of sufficiently suppressingthe pushing-out unless a high elastic modulus can be maintained at theelevated temperature even in the cord having a high elasticity at theroom temperature.

In the pneumatic radial tire according to the invention, thepolyethylene terephthalate cord used in the belt reinforcing layer hasan elastic modulus of not less than 2.5 mN/dtex·% under a load of 29.4 Nmeasured at 160° C. The pushing-out degree of the belt in the high-speedrunning can be suppressed by rendering the elastic modulus of the cordat 160° C. under a load of 29.4 N into not less than 2.5 mN/dtex·%, andhence the stress at the leading-trailing time of the tire can bedecreased to improve the high-speed durability. Therefore, thedeterioration of the high-speed durability due to the lack of theadhesiveness between the cord and the rubber as compared to the nyloncords can be sufficiently compensated to develop the sufficienthigh-speed durability.

In the pneumatic radial tire of the invention, the polyethyleneterephthalate cord used in the belt reinforcing layer is preferable tobe subjected to a dipping treatment under a high tension in order toimprove the elastic modulus at 160° C. The inventor has examined thehigh-speed durability when the tension applied to the cord in thedipping treatment is adjusted to prepare polyethylene terephthalatecords having various elastic moduli and the resulting dipped cords arerubberized and applied to the belt reinforcing layer, and as a result,it has been discovered that the deterioration of the high-speeddurability due to the lack of the adhesiveness can be compensated byimproving the effect of suppressing the pushing-out through the increaseof the elastic modulus when the elastic modulus under the load of 29.4 Nmeasured at 160° C. reaches 2.5 mN/dtex·%, whereby the high-speeddurability equal to that of the tire using the nylon cords in the beltreinforcing layer can be realized.

In order to make the elastic modulus of the cord sufficiently high, thetension in the adhesive treatment is preferable to be not less than6.9×10⁻² N/dtex. When the tension in the adhesive treatment is less than6.9×10⁻² N/dtex, it is difficult to sufficiently enhance the elasticmodulus of the cord at the high temperature. The method for making theelasticity of the cord high is not limited, but other methods such aslow twisting of the cord and so on may be used. The above adhesivetreatment comprises a dry process, a hot process, a normalizing processor the like, and is conducted by properly adjusting the temperature andtime in addition to the tension. Although the adhesive treatment may becarried out by one-bath treatment or two-bath treatment in theinvention, the two-bath treatment is preferable. In the latter case, itis preferable that the tension of not less than 6.9×10⁻² N/dtex isapplied to the cord in the second bath during the hot process.

The polyethylene terephthalate cord is preferable to have a twistingcoefficient α of 500-2500 defined by the following equation (I):α=T×D ^(1/2)  (I)(wherein α is a twisting coefficient, T is a twisting number and D is atotal fineness (dtex) of the cord). When the twisting coefficient α ofthe cord is less than 500, the restraining force of filaments is weakand the adhesion is insufficient, while when it exceeds 2500, theelastic modulus enough to obtain the effect of suppressing thepushing-out can not be developed.

Moreover, the polyethylene terephthalate cord is preferable to have atotal fineness of 1000-3500 dtex. When the total fineness of the cord isless than 1000 dtex, the elastic modulus enough to obtain the effect ofsuppressing the pushing-out can not be developed, while when it exceeds3500 dtex, the end count can not be thickened and the rigidity per unitwidth can not be ensured sufficiently.

By the way, since a green tire extends in a radial direction of the tireby several % during the vulcanization, if the elastic modulus of thecord used in the belt reinforcing layer is high, the cord cannot followthe extension of the tire during the vulcanization and there is apossibility that the cords in the belt reinforcing layer directly comein contact with the steel cords in the belt via no rubber. For this end,it is necessary that the gauge between the belt and the cord issufficiently ensured by previously designing the diameter of the greentire to have a certain size and also by properly adjusting the tensionin the formation of the belt reinforcing layer by spirally winding therubberized cord. Therefore, the polyethylene terephthalate cord ispreferable to have an elongation percentage of not more than 2% in thetire after vulcanization with respect to an original length of the cordbefore vulcanization. When the tire is formed under the elongationpercentage of the cord of more than 2%, the polyethylene terephthalatecord comes in contact with the belt and hence it is apt to easily causethe separation failure at the end of the belt during the running.

In the pneumatic radial tire of the invention, it is preferable that thepolyethylene terephthalate cord is treated with an adhesive compositioncomprising a thermoplastic polymer (A), a heat-reactive aqueouspolyurethane resin (B) and an epoxy compound (C), or an adhesivecomposition containing a rubber latex (D) in addition to the abovecomponents (A)-(C), wherein a main chain of the thermoplastic polymer(A) does not substantially have an addition-reactive carbon-carbondouble bond but has at least one crosslinkable functional group as apendant group. The adhesiveness of the cord to rubber at the hightemperature can be improved by treating with the above-mentionedadhesive composition.

Heretofore, the adhesive treatment of the polyethylene terephthalatecord has been performed by a so-called two-bath treatment wherein anepoxy or an isocyanate is applied onto the surface of the cord and aresin (hereinafter referred to as RFL resin) prepared by mixing aresorcin, a formaldehyde and a latex is applied thereon. In such atreatment, however, the resin used in the first bath becomes very hardto increase a strain input to the cord and hence the fatiguecharacteristic of the cord deteriorates. Also, this resin can expressthe sufficient adhesion force between the cord and the rubber at roomtemperature, but has a problem that the adhesion force extremely lowersat the elevated temperature above 130° C. On the contrary, thesufficient adhesion to the rubber can be ensured even at the hightemperature above 180° C. without hardening the cord by using the firstbath mixture comprising the thermoplastic polymer (A) having at leastone crosslinkable functional group as a pendant group but substantiallycontaining no addition-reactive carbon-carbon double bond in the mainchain structure, the heat-reactive aqueous polyurethane resin (B) andthe epoxy compound (C).

The main chain of the thermoplastic polymer (A) mainly has a straightchain structure. As the main chain are preferable ethylenically additionpolymers such as an acrylic polymer, a vinyl acetate based polymer, avinyl acetate-ethylene based polymer and so on, or a polyurethane basedpolymer. However, the thermoplastic polymer (A) is not limited to theethylenically addition polymers and the polyurethane based polymer, asfar as it has a function that the functional group as the pendant groupis crosslinked to control the fluidity of the resin at the hightemperature and ensure the breaking strength of the resin.

As the functional group in the pendant group are preferable an oxazolinegroup, a bismaleimido group, a (blocked) isocyanate group, an aziridinegroup, a carbodiimido group, a hydrazino group, an epoxy group, anepithio group and so on.

As a monomer constituting the ethylenically addition polymer arementioned an ethylenically unsaturated monomer having one carbon-carbondouble bond and a monomer having two or more carbon-carbon double bonds.As the ethylenically unsaturated monomer having one carbon-carbon doublebond are mentioned α-olefins such as ethylene, propylene, butylene,isobutylene and so on; α,β-unsaturated aromatic monomers such asstyrene, α-methylstyrene, monochlorostyrene, vinyl toluene, vinylnaphthalene, sodium styrenesulfonate and so on; ethylenically carboxylicacids such as itaconic acid, fumaric acid, maleic acid, acrylic acid,methacrylic acid, butenetricarboxylic acid and so on and salts thereof;acid anhydrides such as maleic anhydride, itaconic anhydride and so on;unsaturated carboxylates such as methyl (metha)acrylate, ethyl(metha)acrylate, butyl (metha)acrylate, 2-ethylhexyl (metha)acrylate,methoxy polyethylene glycol (metha)acrylate, 2-hydroxyethyl(metha)acrylate, 2-aminoethyl (metha)acrylate and so on; monoesters ofethylenically dicarboxylic acids such as itaconic acid monoethyl ester,fumaric acid monobutyl ester, maleic acid monobutyl ester and so on;diesters of ethylenically dicarboxylic acids such as diethyl itaconate,dibutyl fumarate and so on; amides of α,β-ethylenically unsaturatedacids such as acrylamide, maleic acid amide, N-methylol acrylamide,N-(2-hydroxyethyl) acrylamide, N-methylol methacrylamide,N-(2-hydroxyethyl) methacrylamide, maleic acid amide and so on; hydroxygroup-containing monomers such as 2-hydroxyethyl (metha)acrylate,polyethylene glycol mono(metha)acrylate and so on; unsaturated nitrilessuch as acrylonitrile, methacrylonitrile, fumaronitrile,α-chloroacrylonitrile and so on; vinyl ethers such as methyl vinylether, ethyl vinyl ether and so on; vinyl ketones; vinyl amides;halogen-containing α,β-unsaturated monomers such as vinyl chloride,vinylidene chloride, vinyl fluoride, vinylidene fluoride and so on;vinyl compounds such as vinyl acetate, vinyl valerate, vinyl caprylate,vinylpyridine and so on; addition-polymerizable oxazolines such as2-isopropenyl-2-oxazoline and so on; heterocyclic vinyl compounds suchas vinylpyrrolidone and so on; unsaturated bond-containing silanecompounds such as vinyl ethoxy silane, α-methacryloxypropyl trimethoxysilane and so on. They may be used alone or in a combination of two ormore. In the invention, the thermoplastic polymer (A) is preferablyobtained by radical addition polymerization of these monomers. As themonomer constituting the main chain structure and having two or morecarbon-carbon double bonds are mentioned conjugated diene based monomerssuch as 1,3-butadiene, 2-methyl-1,3-butadiene,2,3-dimethyl-1,3-butadiene, a halogen-substituted butadiene, e.g.chloroprene and so on; and non-conjugated diene based monomers such asvinyl norbornene, dicyclopentadiene, 1,4-hexadiene and so on. They maybe used alone or in a combination of two or more.

The ethylenically addition polymer is composed of units derived from theethylenic unsaturated monomer having one carbon-carbon double bond andthe monomer having at least two carbon-carbon double bond. Thecarbon-carbon double bond reactive with sulfur is preferably not morethan 10 mol % at the monomer composition ratio and more preferably 0 mol%, on the basis of a total amount of the monomers charged.

The method of introducing the crosslinkable functional group into theethylenically addition polymer to prepare the thermoplastic polymer (A)is not particularly limited. For example, there can be adopted a methodwherein an addition-polymerizable monomer having an oxazoline, anaddition-polymerizable monomer having an epoxy group, anaddition-polymerizable monomer having a maleimide, anaddition-polymerizable monomer having a blocked isocyanate group, and anaddition-polymerizable monomer having an epithio group are copolymerizedin the polymerization of the ethlenically addition polymer.

The polyurethane based polymer is a high molecular weight polymer havingin its molecule many bonds resulted from the reaction between isocyanategroup and active hydrogen such as urethane bonds, urea bonds and so onobtained by mainly polyaddition-reacting a polyisocyanate and a compoundhaving two or more active hydrogens. Moreover, the polymer may containnot only the bond resulted from the reaction between the isocyanategroup and the active hydrogen but also an ester bond, an ether bond andan amide bond contained in the molecule of the activehydrogen-containing compound, and an uretodione bond, an carbodiimidogroup produced by the reaction among isocyanate groups, and so on.

As the heat-reactive aqueous polyurethane resin (B) is preferable aresin having at least two heat-dissociative blocked isocyanate groups inits molecule. For example, a heat-reactive aqueous polyurethane compoundrepresented by the following general formula (II):

(wherein A is an isocyanate residue of an organic polyisocyanatecompound having 3-5 functional groups, Y is an active hydrogen residueof a blocking agent compound alienating an isocyanate group by heattreatment, Z is an active hydrogen residue of a compound having at leastone active hydrogen atom and at least one anion producing group in itsmolecule, X is an active hydrogen residue of a polyol compound having2-4 hydroxyl groups and an average molecular weight of not more than5000, n is an integer of 2-4, and p+m is an integer of 2-4 whereinm≧0.25) and so on are particularly preferable.

The epoxy compound (C) may be a compound containing at least two epoxygroups, preferably at least four epoxy groups in its molecule. Compoundshaving an epoxy group and a reaction product of polyalcohol andepichlorohydrin are preferable. As a concrete example of the epoxycompound are mentioned a reaction product of a polyvalent alcohol andepichlorohydrin such as diethylene glycol diglycidyl ether, polyethylenediglycidyl ether, polypropylene glycol diglycidyl ether, neopentylglycol diglycidyl ether, 1,6-hexanediol diglycidyl ether, glycerolpolyglycidyl ether, trimethylolpropane polyglycidyl ether, polyglycerolpolyglycidyl ether, pentaerythritol polyglycidyl ether, diglycerolpolyglycidyl ether, sorbitol polyglycidyl ether or the like; a novolaktype epoxy resin such as phenol novolak type epoxy resin, cresol novolaktype epoxy resin or the like; a bisphenol A type epoxy resin and so on.

The rubber latex (D) is not particularly limited, butvinylpyridine-styrene-butadiene copolymer latex, styrene-butadienecopolymer latex and so on are preferable.

In the treatment of the polyethylene terephthalate cord, it ispreferable to use a treating solution containing the components (A), (B)and (C) as the first bath and a usual RFL solution as the second bath.Also, it is possible to conduct the treatment with a mixed solutioncontaining the components (A), (B), (C) and (D) in only one bath.Moreover, it is preferable that the dry weight ratio of these componentsbased on the dry weight of the adhesive composition is 2-75% in (A),15-87% in (B), 11-70% in (C), and not more than 20% in (D).

The belt reinforcing layer in the radial tire according to the inventionis formed by treating the polyethylene terephthalate cords with theadhesive composition, rubberizing them to form a narrow-width strip andspirally winding the strip continuously in a circumferential directionof the tire. The tire of the invention is not particularly limitedexcept the cord used in the belt reinforcing layer and can bemanufactured by using usual members according to the usual productionmethod.

The pneumatic radial tire of the invention will be described in detailwith reference to the drawing below. FIG. 2 is a cross-sectional view ofan embodiment of the pneumatic radial tire according to the invention.The tire shown in FIG. 2 comprises a pair of bead portions 1, a pair ofside portions 2, a tread portion 3, a carcass 5 toroidally extendingbetween bead cores 4 embedded in the respective bead portions 1, a belt6 disposed on a crown portion of the carcass 5 outward in a radialdirection of the tire and comprised of at least two belt layers, a beltreinforcing layer 7A disposed on the belt 6 outward in the radialdirection so as to cover the belt 6, and a pair of belt reinforcinglayers 7B disposed so as to cover only both end portions of the beltreinforcing layer 7A. In this case, each of the belt reinforcing layers7A, 7B is composed of a rubberized layer containing cords substantiallyarranged in parallel to the circumferential direction of the tire.Although the illustrated tire comprises the belt reinforcing layers 7A,7B, a tire in which either of the belt reinforcing layers 7A, 7B isomitted is also an embodiment of the tire according to the invention. Inthe illustrated tire, each of the belt reinforcing layers 7A, 7B iscomposed of one layer, but it may be composed of two or more layers.

The following examples are given in illustration of the invention andare not intended as limitations thereof.

EXAMPLES

Cords shown in Table 1 are subjected to a dipping treatment in atwo-bath system. A first bath in the dipping treatment comprises 16.5mass % (solid content) of EPOCROS K1010E (made by Nippon Shokubai Co.,Ltd., solid content: 40%, acryl-styrene copolymer emulsion having2-oxazoline group, Tg of polymer: −50° C., amount of oxazoline group:0.9 mmol/g.solid), 6 mass % (solid content) of ELASTRON BN27 (made byDAIICHI KOGYO SEIYAKU Co., Ltd., solid content: 30%, heat-reactiveaqueous polyurethane resin having a molecular structure of methylenediphenyl), 7.5 mass % of DENACOL EX614B (made by NAGASE Chemicals Ltd.,sorbitol polyglycidyl ether) and 70 mass % of water.

A second bath in the dipping treatment is prepared by adding 233.15parts by mass of vinylpyridine-styrene-butadiene copolymer latex(JSR0655, made by JSR Corporation, solid content: 41%) and 207.00 partsby mass of styrene-butadiene copolymer latex (JSR2108, made by JSRCorporation, solid content: 40%) to 556.85 parts by mass ofresorcin-formaldehyde aged solution comprising 524.01 parts by mass ofwater, 15.12 parts by mass of resorcin, 16.72 parts by mass of 37%formaldehyde and 4.00 parts by mass of 10% sodium hydroxide, and agingthe mixture at room temperature for 16 hours.

When using the above first bath and the second bath, after the drytreatment is conducted under conditions that a dry temperature of thefirst bath is 205° C., a dry time of the first bath is 60 seconds, atension at the dry treatment in the first bath is 1.2 kg/cord, a drytemperature of the second bath is 150° C., a dry time of the second bathis 160 seconds and a tension at the dry treatment in the second bath is1.2 kg/cord, the hot treatment in the second bath is carried out undertension, temperature and treating time shown in Table 1.

Then, pneumatic radial tires having a tire size of 205/65R15 areprepared by using the above adhesive-treated cords in the beltreinforcing layer. At this moment, the belt reinforcing layer is formedby rubberizing the adhesive-treated cords with a rubber compositioncomprising 60.0 parts by mass of natural rubber, 40.0 parts by mass ofSBR, 45.0 parts by mass of HAF grade carbon black, 2.0 parts by mass ofspindle oil, 3.0 parts by mass of zinc oxide, 1.0 part by mass of anantioxidant (made by OUCHISHINKO CHEMICAL INDUSTRIAL Co., Ltd., NOCRAC6C), 0.8 part by mass of a vulcanization accelerator (made byOUCHISHINKO CHEMICAL INDUSTRIAL Co., Ltd., NOCCELER NZ), 1.0 part bymass of stearic acid and 3.0 parts by mass of sulfur to form a striphaving an end count of 50 cords/5 cm and a width of 5-20 mm and spirallywinding the strip continuously in the circumferential direction of thetire. These tires have the same structure except that the cord havingthe structure shown in Table 1 is subjected to the dipping treatmentunder the conditions shown in Table 1 for use in the belt reinforcinglayer. Moreover, the belt reinforcing layers in these tires have thestructure shown in FIG. 2, in which the belt reinforcing layer 7A iswider than the belt by 5 mm in the widthwise direction of the tire, andthe belt reinforcing layers 7B have a width of 30 mm. With respect tothese tires, the high-speed durability, road noise and flat spot areevaluated by the following methods to obtain results shown in Table 1.

(1) High-Speed Durability

The tire is assembled onto a rim of 6J-15 and inflated under an airpressure of 200 kPa and then run at a speed of 150 km/h for 30 minutes,and thereafter the speed is increased every 6 km/h unless the trouble isnot caused to measure a speed of causing the trouble. The result isshown by an index on the basis that the speed of causing the trouble inComparative Example 1 is 100. The lager the index value, the higher thedurable limitation speed and the better the high-speed durability.

(2) Road Noise

In an anechoic room, the tire inflated under an air pressure of 200 kPais run on a drum having a rough surface and a diameter of 3 m at a speedof 60 km/h under a load of 4.7 kN, during which a sound pressure levelis measured with a microphone arranged near to the surface of the drum.The result is shown by an index on the basis that the sound pressurelevel of Comparative Example 1 is 100. The lager the index value, thelower the road noise and the better the road noise.

(3) Flat Spot

After the tire is run on a drum for a predetermined time to sufficientlyraise tire temperature and left to stand until the tire is completelycooled under loading, the deformation of the tire is measured andevaluated as a change of roundness. That is, the roundness is measuredbefore and after the loading respectively, and the difference betweenthe measured values is determined as a flat spot quantity. The result isshown by an index on the basis that the flat spot quantity ofComparative Example 1 is 100. The lager the index value, the lower theflat spot quantity and the better the flat spot.

TABLE 1 Comparative Comparative Comparative Example 1 Example 2 Example3 Example 1 Example 2 Example 3 Material of Cord used in Belt — NylonNylon PET PET PET PET Reinforcing Layer Cord Structure dtex 1400/21100/2 1100/2 1100/2 1100/2 1670/2 Twisting Number number/100 mm 13 × 1347 × 47 47 × 47 47 × 47 26 × 26 39 × 39 (Cable Twist × Ply Twist)Twisting Coefficient — 688 2204 2204 2204 1219 2254 Tension in hottreatment of ×10⁻² N/tex 5.20 2.67 3.57 8.92 8.92 8.92 second bathTemperature in hot treatment ° C. 230 240 240 240 240 240 of second bathTreating time in hot treatment seconds 180 280 280 280 280 280 of secondbath Intermediate Elongation under % 4.84 4.40 3.33 2.68 2.26 1.84 aload of 44 N at room temperature Elastic modulus under a load mN/dtex ·% 1.34 2.10 2.41 2.63 3.87 4.52 of 29.4 N at 160° C. Elongationpercentage of cord % 2.5 2.2 2.0 1.9 1.7 1.5 after vulcanizationHigh-speed Durability Index 100 85 97 110 117 112 Road Noise Index 100102 105 107 113 110 Flat Spot Index 100 104 107 123 134 142

As seen from Example 1 in Table 1, the elastic modulus of the cord undera load of 29.4 N measured at 160° C. can be made to not less than 2.5mN/(dtex·%) by using PET instead of nylon as a material of the cord andmaking a tension at the hot treatment in the second bath to not lessthan 6.9×10⁻² N/dtex, and the high-speed durability of the tire can beimproved by using the cord in the belt reinforcing layer as comparedwith the tire using the nylon cord in the belt reinforcing layer(Comparative Example 1). Also, the road noise and flat spot in the tireof Example 1 are improved because PET is used instead of nylon as amaterial of the cord.

On the contrary, although the road noise and flat spot are improved inthe tires of Comparative Example 2 and 3 wherein the tension in the hottreatment of the second bath is low, the high-speed durability isinferior to that of Comparative Example 1 because the elastic modulus isinsufficient and the deterioration of the high-speed durability due tothe deterioration of the adhesiveness can not be compensated.

1. A pneumatic radial tire comprising a radial carcass, a belt disposedoutside a crown portion of the carcass in a radial direction andcomprised of at least two belt layers, and a belt reinforcing layerdisposed outside the belt in the radial direction, characterized in thatthe belt reinforcing layer is formed by continuously and spirallywinding a polyethylene terephthalate cord(s) in a circumferentialdirection of the tire, and this cord has an elastic modulus of not lessthan 2.5 mN/dtex·% under a load of 29.4 N measured at 160° C.
 2. Apneumatic radial tire according to claim 1, wherein the cord is treatedwith an adhesive composition comprising a thermoplastic polymer (A), aheat-reactive aqueous polyurethane resin (B) and an epoxy compound (C),wherein a main chain of the thermoplastic polymer (A) does notsubstantially have an addition-reactive carbon-carbon double bond buthas at least one crosslinkable functional group as a pendant group.
 3. Apneumatic radial tire according to claim 2, wherein the main chain ofthe thermoplastic polymer (A) is composed of an ethylenically additionpolymer mainly having a straight-chain structure and/or a polyurethanebased polymer, and the crosslinkable functional group as a pendant groupis at least one selected from the group consisting of an oxazolinegroup, a bismaleimido group, an isocyanate group, an aziridine group, acarbodiimido group, a hydrazino group, an epoxy group and an epithiogroup.
 4. A pneumatic radial tire according to claim 2, wherein the mainchain of the thermoplastic polymer (A) is composed of an ethylenicallyaddition polymer mainly having a straight-chain structure and/or apolyurethane based polymer, and the crosslinkable functional group as apendant group is at least one selected from the group consisting of anoxazoline group, a bismaleimido group, a blocked isocyanate group, anaziridine group, a carbodimido group, a hydrazine group, an epoxy groupand an epithio group.
 5. A pneumatic radial tire according to claim 1,wherein the cord is treated with an adhesive composition comprising athermoplastic polymer (A), a heat-reactive aqueous polyurethane resin(B), an epoxy compound (C) and a rubber latex (D), wherein a main chainof the thermoplastic polymer (A) does not substantially have anaddition-reactive carbon-carbon double bond but has at least onecrosslinkable functional group as a pendant group.
 6. A pneumatic radialtire according to claim 5, wherein the main chain of the thermoplasticpolymer (A) is composed of an ethylenically addition polymer mainlyhaving a straight-chain structure and/or a polyurethane based polymer,and the crosslinkable functional group as a pendant group is at leastone selected from the group consisting of an oxazoline group, abismaleimido group, an isocyanate group, an aziridine group, acarbodiimido group, a hydrazino group, an epoxy group and an epithiogroup.
 7. A pneumatic radial tire according to claim 5, wherein the mainchain of the thermoplastic polymer (A) is composed of an ethylenicallyaddition polymer mainly having a straight-chain structure and/orpolyurethane based polymer, and the crosslinkable functional group as apendant group is at least one selected from the group consisting of anoxazoline group, a bismaleimido group, a blocked isocyanate group, anaziridine group, a carbodiimido group, a hydrazine group, an epoxy groupand an epithio group.
 8. A pneumatic radial tire according to claim 1,wherein the cord is subjected to an adhesive dip treatment under atension of not less than 6.9×10⁻² N/dtex.
 9. A pneumatic radial tireaccording to claim 1, wherein the cord has a twisting coefficient α of500-2500 defined by the following equation (I):α=T×D ^(1/2)  (I) wherein α is a twisting coefficient, T is a twistingnumber and D is a total fineness (dtex) of the cord.
 10. A pneumaticradial tire according to claim 1, wherein the cord has an elongationpercentage of not more than 2% in the tire after vulcanization withrespect to an original length of the cord before vulcanization.
 11. Apneumatic radial tire according to claim 1, wherein the cord has a totalfineness of 1000-3500 dtex.